242 ACROSALENIA. 



forms of Acrosalenia hemicidaroides (PI. XV, fig. 4), but from these it is distinguished by 

 having fewer primary tubercles in each row, the two equatorial pairs are disproportionately 

 larger than the others, and those on the upper surface are rudimentary; the apical disc like- 

 wise is smaller, and the sur-anal plate is composed of three pieces, whilst in A. hemicidaroides 

 it has six elements. 



It is distinguished from Acrosalenia spinosa in having fewer primary tubercles in the 

 inter-ambulacral areas, in having the ambulacral areas sinuous, the sur-anal plate with 

 three elements, A. spinosa having only one (PL XVII, fig. 3 /) ; it is so entirely distinct 

 from other congeneric forms that it is unnecessary to make a comparison with them. 



Locality and Stratigraphical position. — This urchin was collected from the Forest 

 Marble at Malmesbury, and belongs to the British Museum ; the honour of detecting the 

 species is due to Mr. Woodward, who has kindly communicated it for this work. 



I have much pleasure in associating the name of my friend Josiah Graham Lowe, Esq., 

 of Kensington Park, Mith this Porest Marble species, as a tribute of gratitude for his kind- 

 ness in presenting me with several rare and valuable specimens for this Monograph, and 

 as an acknowledgment of the valuable service be ^has rendered to the palaeontology of the 

 Porest Marble and Cornbrash formations, so well developed in Wiltshire, in making the 

 finest collection extant from these rich fossiliferous deposits 



Acrosalenia pustulata, Forbes. PI. XVI, fig. 2 a, b, c, d, e,f, g. 



Acrosalenia pustulata. Forbes, Memoirs of the Geological Survey, Decade lY. Notes 



to pi. 3. 



— — Forbes, in Morris's Catalogue of British Fossils, 2d ed., p. 70. 



— — Desor, Synopsis des Echinides FossHes, p. 143. 



Test hemispherical, depressed; ambulacral areas narrow, with two rows of small 

 tubercles disposed alternately, rather wide apart, on the sides of the area ; inter-ambulacral 

 tubercles large at the equator, gradually diminishing towards the peristome, suddenly 

 diminishing on the upper surface ; miliary zone with four rows of granules ; apical disc 

 small, sur-anal plate composed of many pieces ; mouth opening large ; peristome nearly 

 equally decagonal, notches wide ; spines long, slender, tapering ; stem flattened, ring 

 prominent, strise wide apart. 



Dimensions. — Height, half an inch ; transverse diameter, one inch. 



As the [Size of this urchin varies very much, I have selected fom* specimens, from 

 diffierent locaUties in Northamptonshire, and have given their measurements in the follow- 

 ing table — 



